Peripheral leukocyte subpopulations and catecholamine levels in astronautsas a function of mission duration

Objective: The objective of this study was to determine the effects of spac eflight duration on immune cells and their relationship to catecholamine le vels. Methods: Eleven astronauts who flew aboard five different US Space Sh uttle flights ranging in duration from 4 to 16 days were studied before lau nch and after landing. Results: Consistent with prior studies, spaceflight was associated with a significant increase in the number of circulating whi te blood cells (p < .01), including neutrophils (p < .01), monocytes (p < . 05), CD3(+)CD4(+) T-helper cells (p < .05), and CD19(+) B cells (p < .01). In contrast, the number of CD3(-)CD16(+)56(+) natural killer cells was decr eased (p < .01). Plasma norepinephrine levels were increased at landing (p < .01) and were significantly correlated with the number of white blood cel ls (p < .01), neutrophils (p < .01), monocytes (p < .01), and B cells (p < .01). Astronauts who were in space for approximately 1 week showed a signif icantly larger increase on landing in plasma norepinephrine (p = .02) and e pinephrine (p = .03) levels, as well as number of circulating CD3(+)CD4(+.) T-helper cells (p < .05) and CD3(+)CD8(+) T-cytotoxic cells (p < .05) as c ompared with astronauts in space for approximately 2 weeks. Conclusions: Th e data suggest that the stress of spaceflight and landing may lead to a sym pathetic nervous system-mediated redistribution of circulating leukocytes, an effect potentially attenuated after longer missions. Key words: spacefli ght, leukocytes, lymphocytes, catecholamines, stress.